add require.cache

doc/api.markdown

@@ -3243,6 +3243,10 @@ a directory.
 paths onto it, or at startup with the `NODE_PATH` environmental
 variable (which should be a list of paths, colon separated).
 
+The second time `require('foo')` is called, it is not loaded again from
+disk. It looks in the `require.cache` object to see if it has been loaded
+before.
+
 
 ## Addons
 

src/node.js

@@ -268,6 +268,7 @@ var module = (function () {
     require.extensions = extensions;
     // TODO: Insert depreciation warning
     require.registerExtension = registerExtension;
+    require.cache = moduleCache;
 
     var dirname = path.dirname(filename);